Stem cells, in particular pluripotent stem cells such as ES cells and iPS cells, are receiving worldwide attention for their potential application to regenerative medicine. The culture and maintenance of stem cells without loss of their pluripotency usually requires the presence of feeder cells in their culture system, and as such feeder cells, mouse embryonic fibroblasts (MEFs) whose division has been arrested by radiation or antibiotic treatment are used. However, the use of feeder cells is a great restriction on clinical application of human stem cells.
For application of human stem cells to regenerative medicine, a feeder-free (no feeder cells are used) and xeno-free (no xenogeneic components are contained in the culture system) culture environment is required. The present inventors previously found that recombinant human laminins (particularly, laminin 332, which consists of α3, β3 and γ2 chains, and laminin 511, which consists of α5, β1 and γ1 chains) are effective for maintaining the pluripotency of human ES cells (see Non Patent Literature 1), and proposed that a recombinant human laminin E8 fragment or a modified laminin in which a cell adhesion molecule and/or a growth factor binding molecule is conjugated to the recombinant human laminin E8 fragment can be used as an extracellular matrix which enables maintenance culture of stem cells while supporting the retention of their pluripotency (see Patent Literature 1 and 2 and Non Patent Literature 2).
Following the maintenance culture of human stem cells, they should be differentiated to form a three-dimensional tissue structure for their application to regenerative medicine. In the case where cells isolated from a tissue are made to form a three-dimensional tissue structure, a conventionally used extracellular matrix is Matrigel (registered trademark), the trade name for a crude extract of mouse EHS sarcoma, which is known for excessive production of basement membrane components. However, Matrigel is of murine origin and thus is problematic in terms of safety for human use. Collagen gel is also widely used as an extracellular matrix for the three-dimensional culture system, but when collagen gel is used alone, the formation of a three-dimensional tissue structure from human stem cells is hardly achieved due to its poor ability to maintain stem cells. That is, under the current circumstances, there is no appropriate extracellular-matrix material to serve as an alternative to Matrigel for the formation of a three-dimensional tissue structure. Therefore, the speedy development of extracelluiar-matrix materials for the formation of a safe three-dimensional tissue structure for regenerative medicine in humans is strongly desired.